(1) Field of the Invention
This invention relates to pyrido[1,2-a]pyrimidine derivatives and physiologically acceptable salts thereof, a process for preparing such compounds, and pharmaceutical compositions containing such a compound as an active ingredient. The pyrido[1,2-a]pyrimidine derivatives and physiologically acceptable salts thereof in accordance with the present invention have a marked antagonistic effect on slow-reacting substance of anaphylaxis (hereinafter abbreviated as SRS-A) and, therefore, can be used as drugs for the treatment of Type I allergic diseases induced by SRS-A.
(2) Description of the Prior Art
SRS-A is strongly effective in causing contraction of smooth muscle and constitutes a substance responsible for Type I allergic diseases, particularly bronchial asthma and allergic rhinitis [Quarterly Journal of Experimental Physiology, Vol. 30, p. 121, 1940]. Leukotriene D.sub.4 has been found to be a representative active component of this substance and the presence of an inhibitory effect on the in vivo activity of leukotriene D.sub.4 is now considered to be a criterion of the usefulness of a drug for the treatment of Type I allergic diseases induced by SRS-A [Nature, Vol. 288, p. 484, 1980].
Drugs useful for the treatment of Type I allergic diseases induced by SRS-A are roughly divided into two types: drugs of the SRS-A release suppression type which act to prevent the release of SRS-A from mast cells or basophils and thereby inhibit its activity indirectly, and drugs of the SRS-A antagonistic type which act to antagonize the released SRS-A in the living body and thereby inhibit its activity directly. However, drugs of the SRS-A release suppression type are inherently used for the purpose of preventing the induction of allergic attacks by SRS-A and generally tend to lack in effectiveness immediately after the onset of an attack. That is, they often fail to exhibit the so-called rapid-acting property. In recent years, therefore, it has been eagerly desired from the viewpoint of an immediate effect on allergic attacks to develop a satisfactorily effective drug of the SRS-A antagonistic type.
9-Methyl-3-(1H-tetrazol-5-yl)-4H-pyrido[1,2-a]pyrimidin-4-one potassium salt (hereinafter abbreviated as Compound TBX) is a conventionally known pyridopyrimidine compound and it has been reported that this compound is useful for the prevention of Type I allergic reactions (Japanese Patent Laid-Open No. 36294/'79).